**2.1.1 Fermentation medium and experimental system**

Two identical Plexiglas laboratory-scale UASB reactors (R0 and RFe) with a working volume of 2.05 L each, one packed with spiral elements made of steel wire with an iron content of 48% (Fig.1; Table 1), were run in parallel at a constant mesophilic temperature of 35ºC ± 1ºC throughout a 219-day period. Four running stages were identified in term of OLR applied (Table 1). The OLR was increased stepwise from the initial 2.0 kg COD m-3 d-1 to finally 12.0 kg m-3 d-1. The reactors were operated for 25 – 66 days to ensure the reactors reached steady states at each stages (the steady-state conditions were evidenced when the standard deviations of COD removal efficiencies were within 3%). After the steady-state conditions were achieved, the OLR was increased to the next level. HRT at all stages was 48 h. The pH in the reactors was controlled at the level of 7.0 ±0.05 with 2 M NaOH.

Fig. 1. Schematic of the laboratory-scale anaerobic treatment system

Feasibility of Bioenergy Production from

**2.2 Results and discussion** 

reaction chamber.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Fig. 2. Biogas production rate and CH4 content in biogas

Biogas production (m3

 m-3 d-1)

Ultrafiltration Whey Permeate Using the UASB Reactors 195

The COD removal efficiency, TP removal efficiency, biogas production and composition were markedly influenced by using steel elements as an additional medium in the UASB

During Stage 1, both UASB reactors reached the steady-state after 25 days of operation. No statistically significant differences (p>0.05) were observed between UASB reactor with steel elements (RFe) and UASB reactor without steel elements (R0) in term of the average COD removal efficiency and biogas production rate (Fig. 2; 3). Nevertheless, RFe indicated higher (p<0.05) removal efficiency in phosphate (86.2%) and TP (81.2%) than R0 in which the analyzed values were 1.8% and 22.8%, respectively (Fig. 3). CH4 content in biogas produced in RFe was as high as 67.1% which was higher by 11.9% than in R0 (p<0.05). In Stage 2 and 3 both UASB reactors demonstrated a stable work, but statistically significant differences in the values of all the monitoring parameters between R0 and RFe were noticed (p<0.05). The duration of each stage were 36 and 48 days, respectively. The average TP removal efficiency and phosphate removal efficiency in RFe were higher by 77.7% and 83.7%, respectively than in R0 during Stage 2, and 68.1% and 73.9%, respectively during Stage 3 (Fig. 3). During Stage 2 and 3 high COD removal efficiencies (95.6%, 94.8%, respectively) were remained in RFe, in contrast to that of 84.2% in Stage 2 and 80.1% in Stage 3 in R0 (Fig. 3). The average CH4 content in biogas of 78.0% and biogas production of 2.59 m3m-3d-1 in RFe, in contrast to that of 60.8% and 0.92 m3m-3d-1, respectively in R0 (p<0.05), were observed during Stage 2. In Stage 3, biogas production increased by 1.12 m3m-3d-1 in R0 and 1.2 m3m-3d-1 in RFe, but it was still significantly higher in RFe (3.79 m3m-3d-1) than in R0 (2.04 m3m-3d-1), p<0.05 (Fig. 2). Moreover in that stage, the highest methane content in biogas of 79.8% in RFe and 68.1% in R0 were achieved (Fig. 2). During the last stage it was found the highest biogas production rate in RFe of 4.01 m3m-3d-1, while 1.86 m3m-3d-1 in R0 was observed (p<0.05). The average

2 4 712

Biogas production - RFe Biogas production - R0 CH4 content - RFe CH4 content - R0

OLR (g L-1 d-1)

CH4

content (%)


Table 1. Operation regimes for the parallel UASB reactors with and without steel elements

Both UASB reactors were fed with UF whey permeate from the manufacture of dairy products in Nowy Dwór Gdański, Poland. The characteristics of the wastewater used in this study is shown in Table 2. It was received from the factory once a week, was stored at -20°C and was thawed before used. Prior to being fed into the reactor, the substrate was diluted with tap water in accordance with the required organic loading rate (OLR) to obtain wastewater COD concentrations in the average range of 4 – 24 g COD L-1. Diluting UF whey permeate was maintained at a temperature 4°C until used. The reactors were not supplemented with trace elements.


Table 2. Chemical characteristics of wastewater used

The seeding inoculum was taken from a laboratory mesophilic reactor treating synthetic dairy wastewater. Each UASB reactor was seeded up to biomass content of 70 g total suspended solids - TSS L-1 at a ratio of 20% (by volume). During startup the reactors were operated at an OLR of 1.0 kg COD m-3 d-1 and at a HRT of 48 h for 44 days. During the reactors operation, biogas production and composition (CH4 and CO2), total COD, total phosphorus – TP, phosphate, soluble iron concentration and pH in the effluent were measured three times a week. After the operation time of 219 days, sludge samples from both UASB reactors were collected for the determination of TSS content, TP and total iron contents.
